The blood coagulation cascade is an exquisite example of a responsive self-assembly process in biology.1,2 When a wound is formed, a cascade of self-assembly events occur in blood at the site of the wound. The net outcome is the assembly of the globular protein, fibrinogen, catalyzed by a second protein, thrombin to yield chains of fibrin.3,4 A network of insoluble fibrin chains forms a hemostatic “plug” or clot, which presents a physical barrier to the loss of blood from the wound.1,2 The coagulation cascade is a delicately balanced series of events—if it was to occur too easily, blood clots may form in unwanted areas leading to strokes or other complications.
Scientists have long sought to harness the clotting power of fibrin to create hemostatic dressings or bandages.5-7 Hemostatic dressings that can staunch the bleeding from serious wounds are a pressing need both in civilian trauma centers as well as for military personnel. Indeed, uncontrolled hemorrhage from severe injuries is a leading cause of death among young adults (e.g., accident victims) and it is also responsible for the majority of deaths on the battlefield.8-10 Fibrin-based hemostatic sealants were first-developed in the 1940s and have proven to be quite effective.6,7 For example, one form involves a dry powdered mixture of human fibrinogen and thrombin packed onto a solid bandage backing. When such a bandage is firmly pressed onto a bleeding injury, a strong fibrin seal quickly forms and bleeding is stopped.6 However, fibrin bandages have limited practical applicability in trauma medicine because human fibrinogen and thrombin are highly expensive molecules that are scarce in supply.7 
A need thus exists for an inexpensive hemostatic agent based on widely-available materials that could match the blood-clotting ability of fibrin. Although a variety of hemostats have been brought to market, 5,11-15 none have shown the efficacy of fibrin sealants.11,12 Several products work simply by absorbing the blood at the site of the wound rather than by coagulating the blood.12,14 Recently, a new approach has been put forward by Ellis-Behnke et al.,16 wherein the self-assembly of a synthetic peptide into a nano-fibrous network17 is used to achieve hemostasis independent of the natural coagulation cascade. While this method is promising, the synthetic peptides employed are expensive and difficult to synthesize—therefore their practical viability is unclear. An additional factor to consider with hemostats such as the above is the risk of undesired gelation or clotting, i.e., embolization, in parts of the body that are peripheral to the site of injury.14,18 To mitigate against such risks, it would be desirable to have the hemostat disassemble or “unclot” if and when desired; however, none of the hemostats described in the literature have been shown to have this ability.